Clunk when accelerate!

[superfans]

Car is a Tip 996tt. I've been encountering a clunk at the rear sometimes when I accelerate from a low speed (around 30 mph at 3rd gear). Mechanic was unable to fix the problem. Any idea? :help:

[Loren]

Loose sway bar. Needs to be retightened.

[superfans]

I've taken it to the shop and the mechanic said the engine/tranny mounts are tight. The subframe is ok. The sway bar and U/CV joints are all ok. The "thump" doesn't happen all the time. Sometimes it happens when I accelerate quickly while cruising at a low speed.

[chicagoporsche]

If it is a Tiptronic have someone get in the car, put it in drive while firmly holding the brake (pedal brake). Open the engine lid and watch the engine as they apply gas (while holding the brake down). If the engine has more torque movement than normal I bet you it is one or both of the engine mounts. Just replaced mine and I had your same symptoms with no loose sway bar.

Regards,

Ben

[superfans]

To give a better description of the problem. The sound is more like a metallic "thunk" from the rear around the engine area (it seems to come from underneath the engine, maybe from the exhaust). It doesn't happen all the time. Sometimes it happens when the car accelerate (not WOT) at a cruising speed of around 30 to 40 mph (at 3rd gear and sometimes 4th gear, probably around 2000 rpm). The thunk sound does not seem to be from the transmission coz it is from the rear end of the car. Mech thinks that it could be a backfire but couldn't find the cause of the problem. I am not sure if this "thunk" sound is actually describe by other people as "ping" in the engine (spark shock). Since I have been using high level octane gas so the sound shouldn't be the sound of a detonation (plus it doesn't happen all the time). Any comments or views?

[superfans]

Mech said there is a slight backfire upon acceleration. However, he has not yet able to locate the cause of this backfire. Any views?

[WolfgangK]

... does a backfire produce a metallic "thunk"?

I had a similar problem when I had a Boxster and for almost a year nobody found the culprit. In the end it was a motor mount where the rubber disintegrated from the metal. Under certain conditions it was a metal-metal contact which caused some noise. Very hard to find, as it comes and goes. I even was in Zuffenhausen on the factory 'bump road'.

Maybe worth a look?

Regards

Wolfgang

[Stefan]

There's another clunking sound someone reported a while back. It turned out to be a piece of wood under the carpet in the rear trunk.

I was replacing my tail light assembleys last weekend and I dropped one of the nuts and I had to pull up the carpet to retrieve it. Lo and behold, there was a wooden panel that was loose and certainly would make noise if it was rattling around. I'm going to attach it to the floor with velcro when I get a chance.